[task] Render GitHub workflow dashboard in desktop

[phongndo]

Goal

Replace the desktop scaffold panels with the first GitHub workflow dashboard over the app-server.

Why this matters

The desktop app is Nexgit's visual workflow surface. It should show issue, PR, and repository state through the Rust app-server instead of duplicating GitHub logic in TypeScript.

Command/API target

Use the typed preload path to call app-server methods for auth/repo, issue list, and PR list data.

Depends on

• [task] Add app-server auth and repository status methods #7 for auth/repo state.
• [task] Add app-server issue list and view methods #8 for issue data.
• [task] Add app-server PR list and view methods #9 for PR data.

Out of scope

• Do not call GitHub directly from renderer code.
• Do not implement write actions.
• Do not implement review/check detail panels here.

Definition of done

• Desktop shows current GitHub repo/auth state.
• Desktop shows first issue and PR dashboard sections from app-server data.
• Loading, no-auth, no-repo, empty, and error states are visible and understandable.

Verification

• pnpm desktop:typecheck
• pnpm desktop:build
• Run pnpm desktop:dev and include screenshots or concise manual observations in the PR description.

Contributor notes

Keep the renderer thin. Add app-server methods first when data is missing.